32
32

Jul 20, 2013
07/13

by
Gábor Csányi; Balázs Szendröi

texts

######
eye 32

######
favorite 0

######
comment 0

We draw attention to a clear dichotomy between small-world networks exhibiting exponential neighborhood growth, and fractal-like networks where neighborhoods grow according to a power law. This distinction is observed in a number of real-world networks, and is related to the degree correlations and geographical constraints. We conclude by pointing out that the status of human social networks in this dichotomy is far from clear.

Source: http://arxiv.org/abs/cond-mat/0406070v1

11
11

Sep 18, 2013
09/13

by
Gabor Csanyi; Gabor Domokos

texts

######
eye 11

######
favorite 0

######
comment 0

While static equilibria of flexible strings subject to various load types (gravity, hydrostatic pressure, Newtonian wind) is well understood textbook material, the combinations of the very same loads can give rise to complex spatial behaviour at the core of which is the unilateral material constraint prohibiting compressive loads. While the effects of such constraints have been explored in optimisation problems involving straight cables, the geometric complexity of physical configurations has...

Source: http://arxiv.org/abs/1209.1758v2

11
11

Sep 17, 2013
09/13

by
Gabor Csanyi; Balazs Szendroi

texts

######
eye 11

######
favorite 0

######
comment 0

We study a social network consisting of over $10^4$ individuals, with a degree distribution exhibiting two power scaling regimes separated by a critical degree $k_{\rm crit}$, and a power law relation between degree and local clustering. We introduce a growing random model based on a local interaction mechanism that reproduces all of the observed scaling features and their exponents. Our results lend strong support to the idea that several very different networks are simultenously present in...

Source: http://arxiv.org/abs/cond-mat/0305580v1

16
16

Sep 22, 2013
09/13

by
Gabor Csanyi; T. A. Arias

texts

######
eye 16

######
favorite 0

######
comment 0

We identify the shortcomings of existing ab initio quantum chemistry calculations for the hyperfine couplings in the recently characterized azafullerene, C59N. Standard gaussian basis sets in the context of all--electron calculations are insufficient to resolve the spin density near the cores of the atoms. Using the Projector Augmented Wave method implemented on top of a standard pseudopotential plane--wave density--functional framework, we compute significantly more accurate values for the...

Source: http://arxiv.org/abs/cond-mat/0205198v1

6
6.0

Sep 22, 2013
09/13

by
Gabor Csanyi; T. A. Arias

texts

######
eye 6

######
favorite 0

######
comment 0

We explore a new class of computationally feasible approximations of the two-body density matrix as a finite sum of tensor products of single-particle operators. Physical symmetries then uniquely determine the two-body matrix in terms of the one-body matrix. Representing dynamical correlation alone as a single tensor product results in a theory which predicts near zero dynamical correlation in the homogeneous electron gas at moderate to high densities. But, representing both dynamical and...

Source: http://arxiv.org/abs/cond-mat/9805388v4

5
5.0

Sep 18, 2013
09/13

by
Albert P. Bartók; Risi Kondor; Gábor Csányi

texts

######
eye 5

######
favorite 0

######
comment 0

We review some recently published methods to represent atomic neighbourhood environments, and analyse their relative merits in terms of their faithfulness and suitability for fitting potential energy surfaces. The crucial properties that such representations (sometimes called descriptors) must have are differentiability with respect to moving the atoms, and invariance to the basic symmetries of physics: rotation, reflection, translation, and permutation of atoms of the same species. We...

Source: http://arxiv.org/abs/1209.3140v3

21
21

Jul 20, 2013
07/13

by
Gábor Csányi; Stefan Goedecker; T. A. Arias

texts

######
eye 21

######
favorite 0

######
comment 0

We present a new density-matrix functional within the recently introduced framework for tensor-product expansions of the two-particle density matrix. It performs well both for the homogeneous electron gas as well as atoms. For the homogeneous electron gas, it performs significantly better than all previous density-matrix functionals, becoming very accurate for high densities and outperforming Hartree-Fock at metallic valence electron densities. For isolated atoms and ions, it is on a par with...

Source: http://arxiv.org/abs/cond-mat/0107536v2

6
6.0

Sep 22, 2013
09/13

by
Gabor Csanyi; Sohrab Ismail-Beigi; T. A. Arias

texts

######
eye 6

######
favorite 0

######
comment 0

Based on ab initio calculation, we propose a new structure for the fundamental excitation of the reconstructed 30$^\circ$ partial dislocation in silicon. This soliton has a rare structure involving a five-fold coordinated atom near the dislocation core. The unique electronic structure of this defect is consistent with the electron spin resonance signature of the hitherto enigmatic thermally stable R center of plastically deformed silicon. This identification suggests the possibility of an...

Source: http://arxiv.org/abs/cond-mat/9805328v1

22
22

Sep 19, 2013
09/13

by
Albert P. Bartók; Mike C. Payne; Risi Kondor; Gábor Csányi

texts

######
eye 22

######
favorite 0

######
comment 0

We introduce a class of interatomic potential models that can be automatically generated from data consisting of the energies and forces experienced by atoms, derived from quantum mechanical calculations. The resulting model does not have a fixed functional form and hence is capable of modeling complex potential energy landscapes. It is systematically improvable with more data. We apply the method to bulk carbon, silicon and germanium and test it by calculating properties of the crystals at...

Source: http://arxiv.org/abs/0910.1019v3

9
9.0

Sep 20, 2013
09/13

by
Andriy H. Nevidomskyy; Gábor Csányi; Michael C. Payne

texts

######
eye 9

######
favorite 0

######
comment 0

We investigate the nitrogen substitutional impurity in semiconducting zigzag and metallic armchair single-wall carbon nanotubes using ab initio density functional theory. At low concentrations (less than 1 atomic %), the defect state in a semiconducting tube becomes spatially localized and develops a flat energy level in the band gap. Such a localized state makes the impurity site chemically and electronically active. We find that if two neighboring tubes have their impurities facing one...

Source: http://arxiv.org/abs/cond-mat/0301230v2

15
15

Sep 17, 2013
09/13

by
Brendon J. Brewer; Livia B. Pártay; Gábor Csányi

texts

######
eye 15

######
favorite 0

######
comment 0

We introduce a general Monte Carlo method based on Nested Sampling (NS), for sampling complex probability distributions and estimating the normalising constant. The method uses one or more particles, which explore a mixture of nested probability distributions, each successive distribution occupying ~e^-1 times the enclosed prior mass of the previous distribution. While NS technically requires independent generation of particles, Markov Chain Monte Carlo (MCMC) exploration fits naturally into...

Source: http://arxiv.org/abs/0912.2380v3

21
21

Sep 22, 2013
09/13

by
Livia B. Pártay; Albert P. Bartók; Gábor Csányi

texts

######
eye 21

######
favorite 0

######
comment 0

We describe a method to explore the configurational phase space of chemical systems. It is based on the nested sampling algorithm recently proposed by Skilling [Skilling J. (2004) In AIP Conference Proceedings, vol. 735, p. 395.; Skilling J. (2006) J of Bayesian Analysis 1:833-860.] and allows us to explore the entire potential energy surface (PES) efficiently in an unbiased way. The algorithm has two parameters which directly control the trade-off between the resolution with which the space is...

Source: http://arxiv.org/abs/0906.3544v3

27
27

Sep 22, 2013
09/13

by
Albert P. Bartok; Michael J. Gillan; Frederick R. Manby; Gabor Csanyi

texts

######
eye 27

######
favorite 0

######
comment 0

We show how machine learning techniques based on Bayesian inference can be used to reach new levels of realism in the computer simulation of molecular materials, focusing here on water. We train our machine-learning algorithm using accurate, correlated quantum chemistry, and predict energies and forces in molecular aggregates ranging from clusters to solid and liquid phases. The widely used electronic-structure methods based on density-functional theory (DFT) give poor accuracy for molecular...

Source: http://arxiv.org/abs/1302.5680v1

31
31

Jul 24, 2013
07/13

by
Daniel J. Cole; Mike C. Payne; Gabor Csanyi; S. Mark Spearing; L. Colombi Ciacchi

texts

######
eye 31

######
favorite 0

######
comment 0

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidised Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO2 polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress and interactions with single water molecules of a natively oxidised Si surface model...

Source: http://arxiv.org/abs/0807.3215v1

31
31

Sep 18, 2013
09/13

by
Gabor Csanyi; Chris J. Pickard; B. D. Simons; R. J. Needs

texts

######
eye 31

######
favorite 0

######
comment 0

Motivated by recent experimental work, we use first-principles density functional theory methods to conduct an extensive search for low enthalpy structures of C$_6$Ca under pressure. As well as a range of buckled structures, which are energetically competitive over an intermediate range of pressures, we show that the high pressure system ($\gtrsim 18$ GPa) is unstable towards the formation of a novel class of layered structures, with the most stable compound involving carbon sheets containing...

Source: http://arxiv.org/abs/cond-mat/0611511v1

13
13

Sep 22, 2013
09/13

by
Gabor Csanyi; Torkel D. Engeness; Sohrab Ismail-Beigi; T. A. Arias

texts

######
eye 13

######
favorite 0

######
comment 0

Based on {\em ab initio} calculation, we propose a new structure for the fundamental excitation of the reconstructed 30$^\circ$ partial dislocation in silicon. This soliton has a rare structure involving a five-fold coordinated atom near the dislocation core. The unique electronic structure of this defect is consistent with the electron spin resonance signature of the hitherto enigmatic thermally stable R center of plastically deformed silicon. We present the first {\em ab initio} determination...

Source: http://arxiv.org/abs/cond-mat/0011147v1